The iron, chip breaker, lever cap and iron adjustment mechanisms are mounted on an iron wedge known as the ‘frog’.
The frog is adjustable backwards and forwards to change the gap between the blade and the front of the mouth – the opening in the sole of the plane through which the blade projects. A wide gap is needed for deep cutting and a narrow one for fine cutting.
There are different theories about how it came to be known as the frog. One is that it actually resembles a frog, which is roughly wedge-shaped when sitting; another is that it is positioned just behind the ‘throat’ – the area through which the shavings curl upwards – alluding to having “a frog in one’s throat”.